Weighing systems have been proposed for many years in a security capacity in retail environments. Typically a product code is entered (manually or via a machine bar code reader) and then the purchased product is weighed and packed. The product code directly or indirectly (via a product lookup table database) indicates how much the product should weigh, and possibly, the allowable tolerances from some ideal weight. If the product's actual weight corresponds with the weight indicated by the product code, then the probability that the correct product has been weighed and packed is significantly greater than if no such correspondence is obtained.
There has been particular interest in using weighing systems in a security capacity for retail environments for proposed automated retail point of sale systems. Many retail products contain machine readable bar codes which enable the customer to use a bar code reader to scan product's bar codes which directly or indirectly indicate allowable weight. Ehrat, U.S. Pat. No. 3,836,755, discusses a shopping cart which contains a scanning and weighing apparatus and which in conjunction with an evaluation system evaluates the correspondence of weight with product designation. Mergenthaler, U.S. Pat. No. 4,779,706, and Johnson, U.S. Pat. No. 4,787,467, discuss an automated self-service retail checkout station where customers scan and weigh purchased items. A computer system verifies weight obtained with allowable weight to make sure that the customer is not scanning a cheaper product and then packing the expensive product. Schneider, U.S. Ser. No. 07/584,104, discusses an automated point of sale machine which also requires customers to scan products and then verifies the measured weight against the allowable weight to make sure that the customer is not scanning a cheaper product and then packing the expensive product.
A major limitation of the above inventions is that only one product can be weighed at a time. Essentially, a product must be left on the weighing apparatus long enough for the weighing apparatus to produce a signal giving an adequate representation of weight. The length of time required for an adequate representation of weight is generally 2 to 3 seconds. For certain applications, this time delay may be adequate. However, there are numerous retail applications where a faster weighing time is required. For example, in supermarkets where a human cashier is aided by a bagger, the cashier is generally able to scan 36 items per minute. If an automated point of sale system is to duplicate such productivity, then the automated point of sale system must be able to obtain an adequate representation of weight in effectively less than 2 seconds.